At present, when producing dextrose industrially from starch, the principal glucoamylases employed for the saccharification process are those produced by microorganisms belonging to the genera Rhizopus and Aspergillus. The conditions under which these glucoamylases are employed are pH 5.0 and 55.degree. C. for the enzyme of the Rhizopus microorganism, and pH 4.5 and 60.degree. C. for the Aspergillus microorganism's enzyme. In addition, maximum dextrose content of the hydrozylate is about 96% (dry solids basis) when these glucoamylases react with enzyme liquefied starch at a 30% concentration. One reason that the dextrose yield does not reach 100% is that isomaltose accumulates due to a reverse reaction by these glucoamylases. However, there was recently published a report (U.S. Pat. No. 3,897,305) that the reverse reaction of glucoamylses is extremely small in the vicinity of neutrality and that the dextrose yield can thus be elevated to about 98% by carrying out the reaction at about a neutral pH with the joint use of pullulanase. The pullulanase acts to debranch the starch and increases the rate of glucoamylase action under these nearly neutral conditions. As far as neutral glucoamylases are concerned, only one has been reported to date, that being the glucoamylase produced by the rice blast-causing fungus (Piricularia oryzae; Kazuo Matsuda, et al: Amylase Symposium, Vol. 9, 1974), but this glucoamylase possesses low thermostability and so cannot be employed under industrial conditions.